Our experience with the cloning and expression of cloned genes in Saccharomyces cerevisiae suggests that the recovered yield of correctly folded protein product is greatly improved by the use of a yeast secretion process. This is especially true for proteins that are normally secreted from their natural cell sources. Thus, we propose to fuse the gene for human proinsulin to a variety of yeast promoter and secretion signal sequences, and express it in yeast in an attempt to isolate a strain that secretes commercially viable amounts of proinsulin. A number of mutant yeast strains are available to us that have an increased capacity for the secretion of foreign proteins. These "supersecreting" strains will be tested for their efficacy in secreting proinsulin. Once reasonable yields of secreted proinsulin are obtained, we will analyze its structure in terms of disulfide bond content, amino terminal processing and convertability to insulin.